matplotlib pyplot.show：无效的RGBA

Question

我只需要在3D中绘制散点图。

from mpl_toolkits import mplot3d
from matplotlib import pyplot as plt
ax = plt.axes(projection="3d")
ax.scatter(dots_x, dots_y, dots_z, c='red')
plt.show()

有dots_x，dots_y，dots_z是坐标（python列表）。每次我运行程序，我得到ValueError: Invalid RGBA argument: (1.0, 0.0, 0.0, 0.300088123161615)

我对这个元组一无所知。但如果我使用plot3D而不是scatter3D，我会得到完美的曲线。

完整的错误消息：

Traceback (most recent call last):
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\colors.py", line 166, in to_rgba
    rgba = _colors_full_map.cache[c, alpha]
KeyError: ((1.0, 0.0, 0.0, 0.300088123161615), None)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\backends\backend_qt5.py", line 519, in _draw_idle
    self.draw()
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\backends\backend_agg.py", line 437, in draw
    self.figure.draw(self.renderer)
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\figure.py", line 1493, in draw
    renderer, self, artists, self.suppressComposite)
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\image.py", line 141, in _draw_list_compositing_images
    a.draw(renderer)
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\mpl_toolkits\mplot3d\axes3d.py", line 281, in draw
    reverse=True)):
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\mpl_toolkits\mplot3d\axes3d.py", line 280, in <lambda>
    key=lambda col: col.do_3d_projection(renderer),
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\mpl_toolkits\mplot3d\art3d.py", line 459, in do_3d_projection
    fcs = mcolors.to_rgba_array(fcs, self._alpha)
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\colors.py", line 267, in to_rgba_array
    result[i] = to_rgba(cc, alpha)
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\colors.py", line 168, in to_rgba
    rgba = _to_rgba_no_colorcycle(c, alpha)
  File "C:\Users\bozzy\AppData\Local\Programs\Python\Python36-32\lib\site-packages\matplotlib\colors.py", line 219, in _to_rgba_no_colorcycle
    raise ValueError("Invalid RGBA argument: {!r}".format(orig_c))
ValueError: Invalid RGBA argument: (1.0, 0.0, 0.0, 0.300088123161615)

对不起我的英语不好 ：）

UPD：我的程序有完整的代码

from sympy import *
from mpl_toolkits import mplot3d
from matplotlib import pyplot as plt
import pdb

"""
"""

print ("""dx/dt = f(t,x,y,z)
 dy/dt = g(t,x,y,z)
 dz/dt = r(t,x,y,z)""")

x,y,z,t = symbols('x y z t')

f = eval(input("dx/dt = "))
g = eval(input("dy/dt = "))
k = eval(input("dz/dt = "))

n = int(input("Input number of dots: "))
delta_t = eval(input("Input time 'step': "))

t0, x0,y0,z0 = eval(input("Input initial conditions t0, x0, y0, z0: "))


dots_x = [x0]
dots_y = [y0]
dots_z = [z0]
current_t = t0

k1,k2,k3,k4 = None, None, None, None
m1,m2,m3,m4 = None, None, None, None
j1,j2,j3,j4 = None, None, None, None

for i in range(1,n+1):
    k1 = f.evalf(subs={x: dots_x[i-1], y: dots_y[i-1], z: dots_z[i-1], t:current_t})*delta_t
    m1 = g.evalf(subs={x: dots_x[i-1], y: dots_y[i-1], z: dots_z[i-1], t:current_t})*delta_t
    j1 = k.evalf(subs={x: dots_x[i-1], y: dots_y[i-1], z: dots_z[i-1], t:current_t})*delta_t

    k2 = f.evalf(subs={x: dots_x[i-1]+k1/2, y: dots_y[i-1]+m1/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
    m2 = g.evalf(subs={x: dots_x[i-1]+k1/2, y: dots_y[i-1]+m1/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
    j2 = k.evalf(subs={x: dots_x[i-1]+k1/2, y: dots_y[i-1]+m1/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t

    k3 = f.evalf(subs={x: dots_x[i-1]+k2/2, y: dots_y[i-1]+m2/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
    m3 = g.evalf(subs={x: dots_x[i-1]+k2/2, y: dots_y[i-1]+m2/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
    j3 = g.evalf(subs={x: dots_x[i-1]+k2/2, y: dots_y[i-1]+m2/2, z: dots_z[i-1]+j2/2, t:current_t+delta_t/2})*delta_t

    k4 = f.evalf(subs={x: dots_x[i-1]+k3/2, y: dots_y[i-1]+m3/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
    m4 = g.evalf(subs={x: dots_x[i-1]+k3/2, y: dots_y[i-1]+m3/2, z: dots_z[i-1]+j1/2, t:current_t+delta_t/2})*delta_t
    j4 = g.evalf(subs={x: dots_x[i-1]+k3/2, y: dots_y[i-1]+m3/2, z: dots_z[i-1]+j3/2, t:current_t+delta_t/2})*delta_t

    dots_x.append(dots_x[i-1]+(1/6)*(k1+2*k2+2*k3+k4))
    dots_y.append(dots_y[i-1]+(1/6)*(m1+2*m2+2*m3+m4))
    dots_z.append(dots_z[i-1]+(1/6)*(j1+2*j2+2*j3+j4))
    current_t += delta_t

print (dots_x)
print (dots_y)
print (dots_z)

plt.switch_backend(u"qt5agg")
ax = plt.axes(projection="3d")
# pdb.set_trace()
ax.scatter(dots_x, dots_y, dots_z, c='red')
plt.show()

样本输入：

dx/dt = y - x 
dy/dt = x*(28-z) - y 
dz/dt = x*y - z 
number of dots: 500 
time step: 0.1 
initials: 0, 1, 1, 1 

Answer 1

问题似乎是我的matplotlib（Windows 10，Python 3.6.5，matplotlib 2.2.3，sympy 1.1.1，Eclipse / PyDev）和你的环境无法正确处理sympy.core.floats。像x_dots这样的列表不包含普通的Python浮点值，而是包含sympy数据格式。我不太了解sympy，所以我不确定，如何正确处理这个问题，但你可以通过在绘图之前转换值来确认这是问题所在：

fx = [float(i) for i in dots_x]
fy = [float(i) for i in dots_y]
fz = [float(i) for i in dots_z]
ax.scatter(fx, fy, fz, c='red')

或者，您可以使用numpy进行转换：

ax.scatter(np.asarray(dots_x, dtype = "float"), np.asarray(dots_y, dtype = "float"), np.asarray(dots_z, dtype = "float"), c='red')

样本输出：

P.S。：刚刚在Ubuntu 18.04，Python 3.6.5，matplotlib 2.2.3，sympy 1.2，Eclipse / PyDev上进行了测试，错误也可以在那里重现。错误也与后端无关 - 我的第一个怀疑。使用Qt5和TkAgg测试时没有区别。